This invention relates generally to turbine cooling systems including one or more rotatably driven turbines for extracting energy from and concurrently reducing the temperature of a gas stream. More particularly, this invention relates to an improved and simplified multiple stage turbine system designed for simultaneous interaction with more than one gas stream.
Turbine cooling systems or turbocoolers in general are relatively well known in the art. Such systems commonly comprise a turbine wheel mounted within an appropriately shaped turbine housing and having a set of vanes positioned along a gas flow path defined by the housing. A relatively high energy gas stream flowing along the gas flow path passes into driving engagement with the turbine vanes to rotatably drive the turbine wheel typically at a relatively high rotational speed. The turbine wheel is normally coupled to and thus rotatably drives a selected load such as an alternator for producing electrical power, or a fan, etc. Accordingly, the driving interaction between the gas stream and the turbine wheel drives the selected load thereby extracting work from the gas stream. At the same time, the gas stream is volumetrically expanded by the turbine wheel to result in a significant reduction in gas stream temperature.
Turbocoolers of the above-identified type are used in many aircraft and spacecraft and other applications wherein a circulating gas stream is utilized to maintain system components at a desired operating temperature. The turbine wheel is designed to reduce the temperature of the gas stream to a specified output temperature, whereupon the cool gas is circulated into heat transfer relation with system heat sources to control the temperature thereof followed by recirculation of the heated gas into driving relation with the turbine wheel. In this manner, the turbocooler provides an effective apparatus for controlling the operating temperature of a wide range of system components such as electrical or electronic components, aircraft or spacecraft cabin space, etc., while beneficially converting at least some of the extracted heat energy to a useful form.
In some specialized cooling applications, multiple heat loads in a system require cooling gas streams at different temperatures and/or different flow rates for proper temperature maintenance. In such applications, multiple turbocoolers can be used to provide the required gas streams for cooling purposes, but the use of multiple turbocoolers undesirably increases the overall complexity and cost of the system while correspondingly decreasing overall system reliability. Alternately, multiple stage turbocoolers have been proposed with multiple turbine wheels mounted on a common shaft adapted for individual interaction with separate gas streams. While this multistage approach advantageously reduces the complexity of the overall multistream cooling system, in comparison with the use of separate turbocoolers, an increased overall shaft length is required resulting in an increased likelihood of encountering destructive critical speeds. Moreover, undesired mixing of the separate gas streams can result. Still further, when cooling gas is required at substantially cryogenic temperatures, previous turbocooler designs have not provided an effective way to isolate the cryogenic gas from heat sources within the turbocooler itself, resulting in limited turbocooler efficiency. Such turbocooler heat sources may include, for example, bearing heat, or heat produced by the driven load such as an alternator or the like.
There exists, therefore, a need for improvements in turbocoolers particularly with respect to providing a simplified turbocooler construction of compact overall size yet including the capability to produce multiple gas streams at different temperatures for cooling purposes. Moreover, there exists a need for an improved turbocooler designed to provide a cryogenic gas stream at a temperature which is substantially independent of internal turbocooler heat sources. The present invention fulfills these needs and provides further related advantages.